Cell Transport

Diffusion

The net movement of particles from an area of higher concentration to lower concentration. Particles move down the concentration gradient.

Factors of Rate of Reaction

Concentration

Temperature

Surface Area

Concentration

The greater the difference in concentration, the faster the rate of reaction. This is because more particles are randomly moving down the gradient than are moving against it.

Temperature

The greater the temperature, the greater the movement of particles as it results in more collisions and therefore a faster rate of diffusion.

Surface Area

The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion.

Diffusion in the Lungs

Oxygen diffuses into the blood through the alveoli, which are covered in capillaries. Carbon dioxide is transferred from the blood to the alveoli through diffusion.

Diffusion in the Small Intestine

Nutrients diffuse into the blood in the capillaries through the villi.

Diffusion in the Gills

Gas exchange occurs in the gills of a fish. Oxygen from water passes over the gills and diffuses into the blood via the gill filaments. Carbon dioxide diffuses from the blood in the gill filaments into the water.

Diffusion in the Leaf

Carbon dioxide that is used for photosynthesis diffuses into the leaves via the stomata. Oxygen and water vapour diffuse out of them.

Osmosis

Water diffuses from a dilute solution to a concentrated solution through a partially permeable membrane. It moves down the concentration gradient.

Osmosis in Plants

Water moves into the cell into the vacuole, causing it to swell, resulting in pressure called turgor which is essential to keep leaves and stems rigid.

Active Transport

The movement of particles from an area of low concentration to an area of higher concentration. It goes against the concentration gradient.

Active Transport in Root Hairs

It is used to absorb mineral ions from the soil where they are usually in a higher concentration.

Active Transport in the Gut

Allows sugar molecules to be absorbed from the small intestine when the sugar concentration is higher in the blood.

RPA: Osmosis

1. Peel off the skin of the potato and use a cork borer to produce three cylinders of potato with the same diameter

2. Use a scalpel to cut the cylinders to a similar length (approx 3cm)

3. Measure the length of each cylinder with a ruler and the mass with a balance

4. Place each cylinder into a test tube

5. Place 10cm³ of 0.5 molar sugar solution in the first test tube, 0.25 molar in sugar solution in the second test tube and distilled water in the third.

6. Leave over night to allow osmosis to occur

7. Remove from the the cylinders and gently remove surface moisture with a paper towel

8. Measure the length and mass of the cylinders again

9. Measure the percentage changes